Method of producing molded elements with parts of different thicknesses from fibrous mixtures

ABSTRACT

A molding method for producing especially plate-shaped elements each of which is provided with a flange or wall portion projecting form one or more of its lateral edges from a mixture of comminuted fibrous materials and a binder, preferable of hot-setting synthetic resins, wherein the part of the mold chamber in which the thin lateral wall portion or portions are molded has a considerably greater width than the final thickness of the wall portion and thus permits the molding mixture to be easily filled uniformly into the entire mold chamber. The mixture in the lateral downwardly projecting chamber part or parts is then first compressed by lateral, horizontally moving dies to the final thickness of the wall portions, whereupon several lower dies are moved independently of each other to press against the thin lower ends of the precompressed wall portions and against the lower side of the material in the main part of the mold chamber to compress the material in the entire mold chamber to the dimensions and shape of the final product.

y 7, 1974 E. E. MUN 3,809,736

METHOD OF PRODUCING MOLDED ELEMENT.) ITH PARTS OF DIFFERENT THICKNESSES FROM FIBROUS MIXTURES Original Filed April 28, 1969 United States Patent 3,809,736 METHOD OF PRODUCING MOLDED ELEMENTS WITH PARTS OF DIFFERENT THICKNESSES FROM FIBROUS MIXTURES Edmund E. Munk, Oberstenfeld, Germany, assignor to Furnier & Sperrholzwerk J. F. Werk Jr. K.G., Werzalit- Pressholzwerk, Oberstenfeld, Germany Original application Apr. 28, 1969, Ser. No. 819,880. Divided and this application Oct. 26, 1971, Ser. No. 192,499

Int. Cl. B29 5/06 US. Cl. 264-120 6 Claims ABSTRACT OF THE DISCLOSURE A molding method for producing especially plateshaped elements each of which is provided with a flange or wall portion projecting from one or more of its lateral edges from a mixture of comminuted fibrous materials and a binder, preferably of hot-setting synthetic resins, wherein the part of the mold chamber in which the thin lateral wall portion or portions are molded has a considerably greater width than the final thickness of this wall portion and thus permits the molding mixture to be easily filled uniformly into the entire mold chamber. The mixture in the lateral downwardly projecting chamber part or parts is then first compressed by lateral, horizontally moving dies to the final thickness of the wall portions, whereupon several lower dies are moved independently of each other to press against the thin lower ends of the precompressed wall portions and against the lower side of the material in the main part of the mold chamber to compress the material in the entire mold chamber to the dimensions and shape of the final product.

CROSS REFERENCE TO RELATED APPLICATION The present application is a divisional application of the application Ser. No. 819,880, filed Apr. 28, 1969 under the title Mold for Producing Molded Elements with Parts of Different Thicknesses From Fibrous Mixtures, now Pat. No. 3,632,276.

BACKGROUND OF THE INVENTION The present invention relates to a method for producing molded elements of a more intricate shape from a mixture of comminuted fibrous materials, for example, wood chips, and a binder, for example, of hot-setting synthetic resins, and more particularly the invention relates to such a method for producing such molded elements of a substantially plate-like shape wherein each element varies in thickness or height especially by being provided at least at one end with a wall-like portion which is preferably relatively thin but has a relatively great height and projects downwardly from one edge of the plate-shaped part.

Since the mixture to be molded has to be strongly compressed during the molding operation, the mold chamber must have a volume so as to permit an amount of this mixture to be filled therein which depends upon the desired dimensions of the different parts of the element to be molded and their compression ratio which may amount, for example, to 5 to 1. With molding mixtures of this type it is, however, impossible to fill the molding mixture, for example, by hand, into a fixed mold in such a manner that, if the molded product should have abrupt, steplike changes in thickness or height, the mixture will be so uniformly distributed in the different parts of the mold that a uniform rate of compression may be attained by the molding operation. For this reason, it has in the past Patented May 7, 1974 generally been necessary to avoid abrupt or step-like changes in the dimensions of a molded product which was made of fibrous mixtures and to make these changes more gradual. If the changesfrom one wall thickness to another were made too abrupt, the result occurred that in the molding operation of an angular element the area adjacent to the inner corner between two adjacent parts was excessively compressed, while the opposite outer corner of the thicker parts was insufficiently compressed. The degree of solidity of the molded elements was therefore uneven which affected their stability and also caused considerable ditficulties when trying to mold covering layers, for example, of resin-impregnated paper, directly upon the molded elements since due to the insufiicient back-pressure by the insufiiciently compressed parts of the molded element the covering layer was not intimately combined with these parts, while at over-compressed parts of the molded element the pressure upon the covering layer caused the latter to be marked or even damaged.

In order to overcome these disadvantages, efforts were made by the use of limiting inserts to produce molded elements with different wall thicknesses by several successive mold-filling and compressing steps. When employing such a method especially in a hot-molding press, it is, however, impossible to attain a homogeneous combination of the molding materials which are filled into the mold for the different molding stages. Furthermore, after the limiting inserts are removed from the mold, the fibrous mixture which is subsequently added has the tendency to yield laterally during the compressing operation so that the purpose of this method of attaining a uniform compression ratio will not be fulfilled at the corner areas of the molded elements.

As disclosed; for example, by the German Pat. No. 1,165,250, there is another molding method known in which the mold is provided with a plurality of dies which are movable independently of and in opposite direction to each other partly from above and partly from below into and out of the mold chamber. The dies which are movable downwardly from the mold chamber for filling the latter are offset relative to each other in such a manner that on each of them an amount of molding mixture has to be deposited which has a thickness equal to the required multiple of the respective wall portion of the molded element.

This method has the disadvantage that in those cases in which, for example, a part of a molded element should have a small width but a considerable thickness or height, a relatively narrow die has to be retracted very far downwardly in order to attain the desired compression ratio during the molding operation, and that it is very diflicult to fill the fibrous mixture at a uniform rate of distribu tion into this narrow but deep chamber area. Such a change from a small to a great wall thickness or height frequently occurs at the outer edges of molded plateshaped elements.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the mentioned difiiculties and disadvantages of the known methods of molding fibrous mixtures so as to produce especially plate-shaped elements the outer edges of which are provided with thin projecting flanges or wall portions of a height considerably exceeding the thickness of the plate-shaped parts, to make these thin but relatively high parts of a uniform consistency and compression ratio, and, if necessary, to permit the corners between them and the plate-shaped parts to be made relatively sharply angular.

According to the present invention these objects are attained by providing the mold for carrying out the method not only with upper and lower vertically movable dies and with a stationary or vertically movable mold frame, but in addition with one or more dies which are movable laterally within the frame and permit the part of the molded chamber into which the amount of fibrous mixture has to be filled which is required for molding each of the thin or narrow fianges or wall portions to be made of a width and volume which is a multiple of the width and volume of the flange or wall portion in its final compressed condition. For carrying out this method, all of the dies of the mold are retracted for such distances from their final compressing positions that the entire mold chamber is free for receiving the molding mixture and this mixture may be easily filled into the mold chamber from above. Since according to the invention the laterally movable die permits the extension of the chamber which is required for receiving the amount of material which is necessary for molding the thin or narrow but relatively high wall portion to be made considerably wider but less deep than required by the known molds and molding methods, there are now no difficulties in filling the molding mixture uniformly into the entire mold chamber including its extension from the open upper side of the chamber. After the entire mold chamber has been filled with the molding mixture, the upper die is at first lowered upon the mold frame so as to close the mold chamber completely. Then as the next step in the molding operation, the lateral die or dies are moved inwardly into the chamber extension so as to compress the molding mixture therein to the final width or thickness of the downwardly projecting wall portion. According to one embodiment of the invention, each of the lower dies is thereafter moved upwardly within the stationary frame to its final position in accordance with the desired final thickness or height of the plate-like part and of the wall portion on one or both of its lateral ends which has been precompressed by the lateral die or dies. Instead of moving the lower dies upwardly after the mold chamber has been filled, the upper die has been lowered upon the mold frame, and the lateral die or dies have been moved toward the inside of the frame so as to compress the molding mixture for the wall portion or portions to their final thickness, the molding action of the lower dies may also be attained by moving the upper die further downwardly after the lateral die or dies have been moved to their final compressing position. The upper die then moves the mold frame downwardly and compresses the molding mixture from above against the upper and lower dies. According to another feature of the invention which is applicable in a similar manner to either of its embodiments, it is advisable to interpose resilient means, for example, a plurality of compression springs between the main lower die or dies for molding the plate-like part and a common plate to which the narrow lower dies are rigidly secured and which is either movable upwardly or forms a stationary base. These springs retard the compressing movement of the main lower die or dies relative to that of the narrow lower dies.

These as well as additional features and advantages of the present invention will become further apparent from the following detailed description thereof which is to be read with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a vertical section of a mold according to the invention in the open position after being filled, while FIG. 2 shows a vertical section of the same mold in the closed and fully compressing position.

DESCRIPTION OF THE PREFERRED- EMBODIMENT FIG. 1 of the drawings illustrates a mold according to the invention in the open position after the upper die 1 has been moved upwardly from the lower mold and the molding mixture 2 has been filled from above into the mold chamber. The lower dies which according to one embodiment of the invention are movable in the upward direction toward the molding mixture 2 comprise a supporting element 3 above which the main die 4 is located. This main die 4 is movably connected to the supporting element 3 by several compression springs 5 so that when during the molding operation the supporting element is moved upwardly, it will at first move the main die 4 upwardly at a lower speed until it engages upon the main die 4. The supporting element 3 further carries narrow dies 6 which extend vertically to the plane of the drawing and are rigidly secured to the supporting element 3. The mold according to the invention further comprises a frame with opposite frame walls 7 having inner faces 13. Recesses 7 are formed in the frame walls 7 extending outwardly from faces 13 in which lateral dies 8 are movable horizontally in the direction of the double arrows X. As illustrated in full lines in the drawings, the frame walls 7 may be of a substantially U-shaped cross section and the lateral dies may be guided by the upper and lower faces 16 and 16' of the recesses. According to a modification of the invention as indicated diagrammatically by dotted lines, the recess in each frame wall 7 may extend to the upper face 14 thereof. In this case, each lateral die would be guided by the lower guide face 16' of the recess and by parts of the lower surface 21 of the upper die 1 after the latter has been moved down upon the upper surfaces of the frame walls 7 so as to close the mold chamber. The driving means for moving the upper die 1, the supporting element 3 and the dies 4 and 6 are not illustrated in the drawings. The lateral dies 9 are preferably driven by hydraulic or pneumatic means 9, as illustrated diagrammatically, and each of these dies 8 may be driven, for example, by two of these driving means. The double arrows y and 2 indicate respectively the directions of the movements of the upper die 1 and of the supporting element 3 and the dies 4 and 6.

For carrying outthe molding process, two different methods may be employed. According to one of these methods as indicated in the preceding paragraph, the vertical molding pressure by; the dies 4 and 6 is exerted by the upward movement of the supporting element 3 and the resulting movement of dies 4 and 6, in which event the frame walls 7 are stationary, while according to the other method the vertical molding pressure is exerted by the upper die 1 toward the dies 4 and 6, in which event the frame walls 7 are vertically movable and depressed by the upper die 1, for example, against the action of springs, while the supporting element 3 which carries the dies 4 and 6 is stationary.

According to either of these methods, the loose molding mixture 2 is poured into the opened lower mold, whereby the lateral chamber areas 10 may also be easily and uniformly filled which are limited by the front faces 17 of the'lateral dies 8, the part of the horizontal wall surface or surfaces of the recess in front of each retracted lateral die 8, the top faces 20 of the narrow lower dies 6, and the parts of the lateral side faces 19, 19' of main lower die 4 which project above the top faces 20 of the narrow dies 6. These chamber areas 10 may be filled completely without difficulties since they are considerably wider than the final width a of these areas and of the wall portions 12 of the molded element, as may be seen by a comparison between FIGS. 1 and 2. The volume of the lateral chamber areas 10 of the open mold is indicated by the arrows a and b' in FIG. 1 in which the width a amounts, for example, to two and a half times the final width 11 of each wall portion 12 of the molded element. The total volume of each chamber area 10 is therefore equal to five times the final volume of each wall portion 12. The molding mixture 2 which is poured from above into the mold chamber upon the upper surface 18 of the main die 4 has a height 0' which is likewise approximately equal to 5 five times the final thickness of the main part of the molded element.

After the entire mold chamber has been completely filled, the upper die 1 is moved downwardly for the required distance so as to engage upon the upper faces 14 of the frame walls 7 which in any event are maintained at this time in a fixed position either by being stationary at all times or, for example, by being supported by springs, not shown, on the supporting element 3 which is then held in a stationary position. As soon as die 1 abuts against the frame walls 7 and thereby closes the mold chamber, the opposite lateral dies 8 are moved to their final positions as indicated by the dotted lines k. The pressure face or front face 17 of each lateral die 8 is then spaced from the adjacent side face 19 or 19' of the lower main die 4 at a distance equal to the final thickness a of the wall portion 12 of the molded element. The molding mixture 2 which was previously filled into each chamber part 10 is thereby compressed approximately to two-fifths of its original volume. After the lateral dies 8 have reached their final inner positions, the molding mixture 2 in the main mold chamber and the precompressed mixture in the chamber parts 10 will be compressed by the main die 4 and by the narrow dies 6. As previously mentioned, this may be accomplished either by moving the supporting element 3 upwardly and thereby also moving the dies 4 and 6 relative to the stationary frame walls 7 and to the upper die 1 which is then maintained in a fixed position on these frame walls or by moving the upper die 1 further downwardly which then depresses the frame walls 7, for example, against the action of springs, and compresses the molding mixture 2 from above against the back pressure of the main die 4 and of the narrow dies 6 on the stationary supporting element 3.

Assuming that the mold is designed so that the supporting element 3 is movable upwardly, while the frame walls 7 are stationary and covered by the upper die 1 in a fixed position, the upward movement of the supporting element 3 is directly transmitted to the narrow dies 6 which then act upon the lower ends of the laterally precompressed wall portions, while due to the compression springs the upward movement of the supporting element 3 will at first result in a slower compressing movement of die 4 until springs 5 are so far compressed that the upper surface of the supporting element 3 abuts against the lower surface of die 4, whereupon the dies 4 and 6 are moved together until the flanges 3' abut against the lower surfaces of the frame walls 7. Springs 5, the number of which depends upon the size of die 4 must have such a strength that the force which is exerted by all of them is smaller than the force which is exerted by the back pressure of the molding mixture upon the die 4 during the first part of the upward movement of supporting element 3. Springs 5 therefore retard the upward movement of die 4 relative to the upward movement of the narrow dies 6 which are rigidly secured to supporting element 3. When the lateral flanges 3' abut against the lower surfaces 15 of the frame walls 7, as shown in FIG. 2, the narrow wall portions 12 and the main part 11 of the molded element will have their predetermined sizes, shapes and densities. If the lateral dies 8 do not have a height, as indicated by the dotted lines in FIGS. 1 and 2, so as to be guided by the lower surfaces of the recesses in frame walls 7 and by parts of the lower surface 21 of the upper die 1 which then engages upon the remainder of the upper surfaces 14 of frame walls 7, but if they have a height h and are guided by the upper and lower surfaces of the recesses, as shown in full lines in the drawings, the upper end surfaces of dies 6 will at the end of the molding operation be located at a short distance above the upper surfaces of the recesses. The molded element then consists of the wide platelike central part 11 of a small thickness 0 which is limited at its opposite ends by the wall portions 12 of a small thickness a and a greater height b.

When the molding operation is completed and the binder in the molding mixture has preferably been set, for example, by heating the mold, preferably while the molding operation is being carried out, the dies 1, 4, 6, and 8 are retracted to their initial positions and the molded element is removed from the mold.

The important feature of the invention of providing the lateral dies 8 in addition to the narrow vertical dies 6 has not only the advantage that they permit the chamber parts 10 to be made of a considerably greater width and lower height than those which were previously required when only narrow vertical dies of a great length were provided, and that these chamber parts 10 may therefore be filled with the molding mixture 2 very uniformly and without any difficulty even by hand, but it has the further important advantage that the total force which is required to compress the molding mixture in these chamber parts 10 first in lateral directions to the final width or thickness of the desired wall portions and then in a vertical direction to the desired length is considerably less than that which was required in the known method for compressing the molding mixture in a very long or high chamber part solely in a vertical direction to the final height and compression ratio of the desired wall portion. Furthermore, it is quite obvious that by first exerting the molding pressure upon the much larger lateral side of the molding mixture in the chamber part 10 and by then only exerting a vertical pressure upon the narrow and relatively short wall portion to attain the desired height thereof, the finally molded material of the wall portion will have a much more uniform density than if the compression is only exerted in a vertical direction upon the molding mixture in a narrow but very high chamber part. Aside from these advantages, there is still another which might even be the most important. When the molding mixture 2 is filled into the entire mold chamber, the fibers of this mixture have the tendency to be oriented in a substantially horizontal direction. If the compression of the mixture in the narrow lateral chamber parts is carried out solely in the known manner in a vertical direction, that is, in a direction at right angles to the direction of the fibers, the substantially horizontal orientation of the fibers in the compressed mixture will remain unchanged. Because of the small width or thickness of the finally molded wall portion, this portion will therefore have a 'very low breaking strength. If, however, the molding of these wall portions is carried out in accordanee with the invention, it has been found that by first exerting a strong lateral pressure upon the molding mixture for these wall portions, the fibers in this mixture will turn from their original horizontal orientation partly to an inclined and partly to an upwardly or downwardly curving shape and become interlocked or felted to each other. This interlocking or felting effect is further increased by the subsequent compression of the laterally precompressed material in the vertical direction. By numerous tests it has been found that the breaking strength of the narrow wall portions which are produced according to the invention far exceeds that of similar wall portions which are solely produced by vertical compression.

Of course, the shape and construction of the mold according to either of the embodiments of the invention as previously described may be considerably modified in accordance with the particular shape and structure of the desired molded product. While in the previous description it is assumed that the molded element consists of a plate with a main central part of a considerable width but small thickness which is provided along each of its opposite sides with a thin wall of a relatively great height, the front and rear sides of this element are not made of any greater thickness or height than the main central part. In this case, the two dies 6 are not connected to each other but movable independent- 7 ly of each other. If, however, the molded element should have along all of its edges a continuous rim or wall either of a uniform thickness and/or height or of a different thickness and/or height at different sides, a single frame-like die 6 may be provided. The stationary frame wall 7 must then be provided with recesses in all four of their inner sides in which lateral dies 8 are movable.

The molded element also does not need to be of a symmetrical shape like that of the element as shown in the drawings, but it may, for example, be provided only on one side or only on a part of one side with a thin wall or wall portion of a greater height or this thin wall or wall portion may vary in thickness and/or height in its longitudinal direction. This may then require two or more independent lateral dies in the same frame wall 7. It is further possible according to the invention to produce molded elements of a more intricate shape by employing several independently movable lower dies in place of the single central die 4 as shown in the drawing. These individual dies are then designed to produce adjacent horizontal molded parts of different thicknesses and the compression stroke of each of these dies is made of a length in accordance with the desired rate of compression of the respective molded part or of all horizontal parts. Furthermore, the upper die 1 may be designed so as to move from above for a certain distance between the stationary frame walls 7. This die 1 may then be'provided, for example, with a projection on its lower side the outer dimensions of which correspond with the inner dimensions between the frame walls 7 and the lower surface of which forms the pressure surface which engages upon the molding mixture 2 in the mold chamber, while the outer ends of the upper die 1 by engaging upon the upper surfaces of the frame walls 7 limit the depth to which the projection of die 1 can pass into the mold chamber and compress the molding mixture 2 therein from above.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, 1 wish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

1. A method of molding a compacted and bonded element having a plate-like main part and a wall portion of smaller width than said main part and projecting transversely from one side edge of said main part, from a mixture of comminuted fibrous material and a binder, comprising (a) filling with said mixture a mold chamber having a main chamber portion of an area substantially equal to that of said plate-like main part and of a thickness greater than that of said main part, and at least one chamber extension extending outwardly and transversely from one lateral side of said main chamber portion and having a height and width greater than that of said wall portion of said element;

(b) laterally compressing said mixture in said chamber extension in a first direction and to a width equal to that of said wall portion of said element to be molded; and

(c) compressing said mixture in said main chamber portion as well as said laterally compressed mixture in a second direction normal to said first direction to the dimensions desired for said element, so that the mixture originally contained in said chamber extension will be compressed in ,two directions normal to each other and be bonded into said element.

2. The method of claim 1, wherein step (c) comprises:

first compressing said laterally compressed mixture in said second direction to the final dimensions of said wall portion of said element; and

subsequently compressing the mixture in said main chamber portion to the final dimensions of said plate-like main part of said element.

3-. The method of claim 1, wherein said mold chamber has an open upper end, and said chamber extension has a closed upper end and communicates with said main chamber portion at a lower portion of said lateral side, comprising, after step (a):

closing said upper end of said main chamber portion of said mold chamber; and

carrying out step (c) in a direction towards said upper closed end of said mold chamber.

4. The method of claim 3, wherein said mold chamber comprises a frame defining in the interior thereof said main chamber portion, said frame having a top face, a bottom face and a pair of opposite sidewalls spaced from each other a distance at least equal to the width of said main part, at least one of said sidewalls having a recess opening into said main chamber portion, said recess constituting said chamber extension and having a bottom face higher than the bottom face of said frame; and wherein the method comprises, after carrying out step (a),

closing one side of said main chamber portion by two dies movable relative to each other, one of said dies having a width equal to that of said wall portion and having a side face thereof in contact with an inner face of said one side wall of said frame and also having a top face initially flush with said bottom face of said chamber extension, and the other of said dies having one side face in sliding contact with another side face of said one die and extending to ward the opposite side wall of said frame, said other die having a top face upwardly spaced from said top face of said one die and initially spaced from said top face of the frame a distance greater than the thickness of said main portion of said element.

5. The method of claim 4, wherein step (b) comprises:

moving a lateral die having a front face in said chamber extension towards said one side face of said other die until said front face of said lateral die is flush with said inner face of said one side wall of said frame.

6. The method of claim 4, wherein step (c) comprises:

fixedly supporting said one die on a face opposite said top face thereof on a supporting element;

supporting said other die on a face opposite the top face thereof by compression springs sandwiched between said supporting element and said opposite face of said other die; and

moving said supporting element and said frame relative to each other in a direction in which said top faces of said dies move toward the closed end of said mold chamber until the mixture is compressed to the final dimensions of the element being molded.

References Cited UNITED STATES PATENTS 1,776,888 9/1930 Clark 425330 FOREIGN PATENTS 820,327 8/1956 England 425330 692,421 8/1964 Canada 264- DONALD J. ARNOLD, Primary Examiner J. R. HALL, Assistant Examiner US. Cl. X.R. 

